The present letter reported the synthesis of MgO-containing magnetic nanocomposites by calcinations of tailored hydrotalcite-like layered double hydroxides (LDHs) of the type [Mg(1-x-y)Fey(y)(2+)Fe(x)(3+) (OH)(2)](x+)(A)x/2.mH(2)O (y ≥ 0; A = CO32- or SO42-) precursors at 900° C for 2 h. The results indicate that calcination of LDHs gives rise to the formation of magnetic nanocomposites of MgO and MgFe2O4 spinel ferrite, where MgO formed could disperse and separate MgFe2O4 particles, and MgO itself was also dispersed or embedded uniformly in the MgFe2O4 spinel matrix. Furthermore, initial studies on the bactericidal properties with staphylococcus aureus show that these as-synthesized nanometer-sized materials have significant bactericidal effect, which increases with the increasing volume fraction of MgO. (C) 2005 Springer Science + Business Media, Inc.